Engine speed sensors have typically been incorporated on the camshaft or crankshaft of the engine for providing accurate engine and transmission control. In recent rotational speed sensing systems, active encoder wheels have been mounted to the end of the crankshaft, and an active or passive sensor is mounted in close proximity to the encoder wheel by a crankshaft seal retainer plate that is mounted to the engine block. The crankshaft seal retainer plate is required to be cast with precision in order to ensure that the active sensor is precisely mounted with a predetermined air gap between the sensor and the encoder wheel or tone wheel. The engine speed sensor of this type provides precise speed and position measurement for accurate misfire detection. In the typical system which utilizes a cast crankshaft seal retainer plate to support the sensor, the cast part is heavy, bulky and expensive to manufacture.